Field of the Invention
The present invention generally relates to wireless communications networks, such as cellular networks. More particularly, the present invention relates to resources allocation on wireless communication networks, such as OFDMA wideband wireless communication networks making use of a Distributed Antenna System through Frequency Domain Packet Scheduling.
Overview of the Related Art
Evolution of wideband wireless communication networks has experienced a significant growth in terms of spread and performance, and has recently brought to new-generation cellular systems (generally referred to as fourth generation or 4G cellular wireless systems), such as WiMAX (“Worldwide Interoperability for Microwave Access”)—i.e. a communication technology for wirelessly delivering high-speed Internet service to large geographical areas, LTE (“Long Term Evolution”) and LTE-Advanced, which are designed to meet needs for high-speed data and media transport as well as high-quality voice and video communications support into the next decade.
As known, such new-generation cellular systems make use of some advanced techniques, such as OFDM (“Orthogonal Frequency Division Multiplex”) signal transmission scheme—based on using multiple sub-carriers closely-spaced in the frequency domain such that adjacent sub-carriers are orthogonal to each other, and the associated OFDMA “Orthogonal Frequency-Division Multiple Access” access scheme, relying on the use of the OFDM signal transmission scheme and according to which individual (or groups of) sub-carriers (i.e. elementary resource allocations, generally referred to as “Physical Resource Blocks”) are assigned, based on scheduling decisions, to different users, so as to support differentiated Quality of Service (QoS), i.e. to control data rate and error probability individually for each user.
An extension of such OFDMA-based wireless communication networks is to consider the implementation thereof within Distributed Antenna Systems, which, originally introduced to simply cover dead spots in indoor wireless communications networks, have been recently identified as providing potential advantages in outdoor wireless communications networks (to such an extent that many cellular service providers and/or system manufacturers may also consider replacing legacy cellular systems with distributed antenna systems or adopting them in the forthcoming 4G wireless communications networks).
Each Distributed Antenna System (in the following DAS system or DAS, for the sake of conciseness) substantially comprises a network of spatially separated radio-transmitting remote units—e.g. antennas—covering a corresponding geographic area, and a common central unit (or eNodeB), for accomplishing processing and managing operations, to which each remote unit is connected through a proper transport medium (e.g. optical fibers, dedicated wires, or exclusive radio-frequency links). Each remote unit is configured for receiving a digital base-band signal from the central unit, and, after digital to analog conversion, filtering and amplifying operations, for transmitting the corresponding radio-frequency signal to user equipments (e.g., user terminals, such as cellular phones) of subscribers/users requiring services in the same network cell (e.g., voice call). In this way, being the radio-frequency signal to be transmitted by the central unit radiated by several remote units located remote from the central unit, better defined cell coverage and extended cell coverage (thus, fewer coverage holes), simplified maintenance (as DAS system can reduce the required number of central units within a target service area) and higher signal-to-interference-plus-noise ratio (SINR) are obtained with respect to a non DAS system.
Presently, a number of works are known wherein solutions providing for scheduling schemes are disclosed.
In Ping Gong, Ke Yu, Yumei Wang, “Radio resource allocation for multiuser OFDMA distributed antenna systems”, IEEE International Conference on Network Infrastructure and Digital Content, 2009, the authors face the problem of assigning transmitting power and logic sub-bands to a plurality of users served in DAS modality, in downlink direction. The problem of allocation is formulated as problem of mixed integer-linear optimization, and heuristic algorithms are calculated that approximate the optimum solution.
In Joonil Choi, Illsoo Sohn, Sungjin Kim and Kwang Bok Lee, “Efficient Uplink User Selection Algorithm in Distributed Antenna Systems”, IEEE 18th International Symposium on Personal, Indoor and Mobile Radio Communications, 2007, the authors describe a scheme for assigning users to antennas.
In W. Xu, Z. He, K. Niu, “Opportunistic Packet Scheduling in OFDM Distributed Antenna Systems”, WiCOM'09 Proceedings of the 5th International Conference on Wireless communications, networking and mobile computing, 2009, the authors investigate an OFDM system with distributed antennas for allocating power and sub-bands in such a way to minimize packet losses.
In B. Yang, Y. Tang, “Heuristic Resource Allocation for Multiuser OFDM Distributed Antenna System with Fairness Constraints”, Proceedings of ICCTA 2009, the authors face the problem of maximizing the amount of traffic transmitted under some constraints in an OFDM system with DAS. In this respect, the authors propose heuristic algorithms for allocating sub-carriers to the users, with the constraints that an antenna can serve only one user on a sub-carrier and that each user has a predefined granted minimum rate.
In Lisha Ling, Tan Wang, Ying Wang, Cong Shi, “Schemes of Power Allocation and Antenna Port Selection in OFDM Distributed Antenna Systems”, Vehicular Technology Conference Fall (VTC 2010-Fall), 2010 IEEE 72nd, the authors propose a power allocation and antenna port selection heuristic algorithm on OFDM-DAS systems.
In Marsch P., Khattak S., Fettweis G., “A Framework for Determining Realistic Capacity Bounds for Distributed Antenna Systems”, Information Theory Workshop, 2006. ITW '06 Chengdu. IEEE, the authors propose a framework for evaluation of uplink capacity bounds of DAS systems through link-level simulations.
In Jun Zhang, Andrews J., “Distributed Antenna Systems with Randomness Wireless Communications”, IEEE Transactions, 2008, the authors evaluate performance, by simulating a realistic channel, of single-cell and multi-cell DAS systems by comparing two known transmitting techniques (i.e. MRT, or “Maximum Ratio Transmission”, and ST, or “Selection Transmission”), verifying that the single-cell MRT technique provides better performance whereas the multi-cell ST technique provides lower outage probability. Moreover, the authors study how the geometric or random arrangements of the remote units affect the system performance.
In Zhu, H., Karachontzitis, S., Toumpakaris, D., “Low-complexity resource allocation and its application to distributed antenna systems”, Wireless Communications, IEEE 2010, the authors evaluate, through link-level simulations, performance increase in case of resource allocation based on frequency chunk (logical band) in single-cell systems and DAS systems, by comparing two known transmitting techniques (i.e. MRT, or “Maximum Ratio Transmission”, and ZFB, or “Zero Forcing Beamforming”).
In Peng Shang, Guangxi Zhu, Li Tan, Gang Su, Tan Li, “Transmit Antenna Selection for the distributed MIMO Systems”, 2009 International Conference on Networks Security, Wireless Communications and Trusted Computing, the authors face the problem of the selection of the transmitting antenna as a two-level optimization problem: the first level selects the cluster of antennas for the service of a determined user, whereas the second level selects which antennas of the cluster are to be used for the user.
In Alexei Gorokhov, Dhananjay A. Gore, and Arogyaswami J. Paulraj, “Receive Antenna Selection for MIMO Spatial Multiplexing: Theory and Algorithms”, IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL. 51, NO. 11, NOVEMBER 2003, the authors illustrate different algorithms, described for MIMO systems and applicable to DAS systems, for the selection of the receiving antennas in the uplink direction.